During the production of complex assemblies, such as aircraft, there is sometimes a need to monitor assembly operations and verify that certain operations have been properly performed on a subassembly. For example, aircraft landing gear may be controlled by one or more hydraulic systems comprising hundreds of hydraulic tubes and fittings that must be assembled within a relatively small wheel well. Each of these fittings includes a nut that is tightened or “torqued” by an assembly worker to a nominal torque value. Because of the large number of nuts that must be torqued, it is desirable to monitor and verify that all of the nuts have been properly torqued, since the failure to properly assemble fittings, and/or torque nuts to nominal values may result in hydraulic leaks that must be later corrected. Past attempts to verify that nuts have been properly torqued have been limited to the application of marks on the nuts in order to visually indicate that they have been torqued, however this technique may be subject to human error, and in any event, may not allow verification that the nut has been torqued to the correct value.
A variety of techniques have been developed for locating and monitoring objects such as parts and subassemblies in three dimensional space, including those utilizing radio frequency (RF), optic, sonic and chemical communication, however, each has limitations in terms of accuracy and effectiveness within harsh communications environments. For example, known object location systems may be ineffective in those environments where line-of-sight (LOS) to the object is not available, or where structures or surfaces within the environment result in signal reflection and/or attenuation.
Known object location systems may not be well suited for monitoring the proper assembly of the hydraulic tube fittings, because these locating systems may not be capable of either locating the nuts, or locating the nuts with sufficient accuracy to distinguish between closely spaced nuts within a highly confined, crowed environment such as a wheel well. Moreover, the use of RF techniques to monitor nut torquing is particularly challenging due to the adverse effects of multipath caused by the abundance of metallic objects in a wheel well environment, and the complex physical layout of the wheel well which lacks fixed positioning system infrastructure.
Accordingly, there is a need for a system for locating and reporting the condition of objects within a harsh RF environment such as a wheel well in an aircraft.